This invention relates generally to detectors for optical systems, and, more particularly, to a high efficiency fiber-shaped detector capable of detecting intensity, optical path angularity and optical alignment of incoming beams of electromagnetic radiation.
There currently exists many applications in which very wide field of view optical systems are required. One such application is a U.S. Air Force requirement for a very wide field of view optical seeker for air-to-air, air-to-ground and ground-to-air missiles. Other applications include industrial robots, space based sensors and security surveillance cameras.
It is common practice to meet the requirements of these applications with single aperture optical systems. However, since, in the single aperture optical system the focal length is tied to lens diameter (and field of view) the light gathering optics must either be very large, or else, the lens must be scanned in order to provide wide angle field of view surveillance. The size and complexity of systems based on this approach make it impractical for airborne applications. The size and focal length required for a very wide field of view single aperture lens that would function without scanning would of necessity, be too large to be accomodated on a missile. On the other hand, in order to provide scanning, optical domes, gimbals and Cassegrain optical systems would be required. For other applications the cost and complexity associated with single aperture lens systems frequently render that approach impractical.
The above enumerated disadvantages of single aperture optical systems are eliminated by utilizing multiaperture optic principles wherein the aperture is decoupled from focal length and physical space requirements are reduced. The concept of a multiaperture optical system is based on the biologically evolved invertibrate (insect) eye. The invertebrate multiaperture eye and its development and relationship to a mechanical model implementing it are described in detail in the papers Signal Processing In The Insect Eye by J. F. Butler, R. C. Wilkinson, R. T. Schneider and J. F. Long and A Mechanical Model Of The Insect Eye by R. T. Schneider, E. E. Carroll, Jr., G. R. Dalton and J. F. Long presentd at the IEEE SOUTHEASTCON, 1982, Sandestin, Destin Florida, Apr. 4-7, 1982 and published in the IEEE PROCEEDINGS thereof. Further details are described in the University of Florida draft Final Report Volume II entitled Multiaperture Optics by Richard T. Schneider, dated 1 Dec. 1982, which report is incorporated herein by reference and is being published as an Air Force Armament Laboratory Formal Report.
The cited references describe two types of multiaperture optics that are useful for the applications indicated above. They are the apposition eye and the neural superposition eye. It is well known and has been demonstrated in the above cited references that image formation can be achieved either by interference or collimation. The latter is mostly used for high energy radiation, where the corresponding wavelengths are too short to be practical for interference systems.
The apposition insect eye is a collimation system. A collimator is often lensless, e.g., for neutrons or gamma particles. Even if a lens is used like in an autocollimator, the property of light which is utilized is the fact that it propagates in a straight line. The apposition eye uses lenses not for image formation, but for definition of the field of view for an individual eyelet. The location of the image point is entirely determined by the fact that the light propagates in a straight line. One consequence of this is the decoupling of the focal length of the eye from the field of view of the eye. The field of view is determined by the curvature of the surface of the multiaperture eye. For the single aperture eye this surface is already utilized for determination of the optical properties of the lens rather than for definition of the field of view which is now determined by the focal length (for a given f-number and a given eye diameter). The consequence is that in the case of the multiaperture system the focal length can be kept extremely short, which provides for a minimum depth for the total eye.
Another difference between interference and collimating optics is the curvature of the image plane (retina). For the apposition eye the curvature of the retina is always convex while it is concave for a single lens eye. If the multiaperture system is to be mounted on a surface (like the skin of a missile) the convex curvature makes this possible. The disadvantage of the apposition eye is the limited resolving power which, however can be made good by using a very large number of eyelets.
The neural superposition eye is no longer a collimation system but an interference system. It forms a small image. Since an image is formed, the question is why not use one lens only and obtain better resolving power. Obviously the neural superposition eye should be only used for special applications where details of the image are not important. This eye necessarily must be target oriented and not detail oriented. If it is necessary to identify a target as such and to determine where it is located rather than to describe differences in similar targets then the neural superposition eye has advantages over the single aperture eye. The advantages discussed above for the apposition eye still apply to some degree for the neural superposition eye, namely the decoupling of the field of view from the focal length and the convex shape of the retina.
Based on the above discussed fact, it can be seen that multiaperture optics can be used for specialized applications where the location and recognition of the target is more important than detailed description of the target. Such applications would include all optical systems having space and complexity limiting requirements as with the air-to-air missiles, air-to-ground missiles, ground-to-air missiles, robots, space based sensors, security surveillance cameras mentioned above.
An example of an integrated multiaperture optical system that provides viewing of and object identification in a very large scene without scanning of the light gathering optics is described in U.S. patent application Ser. No. 475,676 filed on Mar. 15, 1983 by the present inventor together with James F. Long. This system has the advantages of having a very large field of view without scanning; greatly reduced space requirements; large scale integrated circuit construction; reduced complexity and manufacturing costs; and improved performance for certain applications. It is particularly suited to U.S. Air Force optical missile seeker applications.
Further, the above-mentioned integrated multiaperture optical system comprehends multiaperture light gathering optics that projects received electromagnetic wave energy onto a detection layer. The output of the detector layer is correlated and then processed by a data processing stage to identify objects of interest in a scene being viewed by the light gathering optics.
The multiaperture light gathering optics includes an array of eyelets, or lens apertures, each viewing a discrete region of the scene under surveillance. The lens aperture members can have optical configuations and orientations that effect either apposition or neural superpostition imaging on the detector layer. The array can consist of either type lens aperture members or a combination of them.
The detector layer comprises a separate detector for each lens aperture member and each detector has a multiplicity of elements with each element having a separate output.
Correlation is achieved in a correlation layer adjacent to the detector layer. It contains a memory for each detector element. There is an amplifier and analog/digital converter combination for each detector element that conditions and loads data received by the detector element into its associated correlation layer memory. Certain memories are interconnected in accordance with a hard wired program to effect neural superposition image processing.
A processing layer adjacent to the correlation layer includes a memory matrix that accesses the correlation layer memories. The data processing layer also includes microprocessor circuitry that processes the data contained in the memory matrix in accordance with an object recognition routine and in accordance with algorithms for apposition and neural superposition modes of operations.
The system is implemented by using very large scale integrated circuit techniques whereby correlation layer memories can be physically located directly below their associated detector elements.
A major undertaking in the development of the above-described optical system involves providing an acceptable, high efficiency detector for use therein. Heretofore, conventionally available detectors were incapable of providing the high efficiency necessary for effective operation of such an integrated multiaperture optical system as described above.